The stadium TFR is about protecting broadcast holder rights by keeping out unauthorized advertisers (i.e. banner tows). My guess is that Wrestlemania wasn't part of the original lobbying effort by the NFL, MLB, NASCAR, etc.

All aircraft operations; including parachute jumping, unmanned aircraft and remote controlled aircraft, are prohibited within a 3NMR up to and including 3000ft AGL of any stadium having a seating capacity of 30,000 or more people where either a regular or post season Major League Baseball, National Football League, or NCAA division one football game is occurring. This NOTAM also applies to Nascar Sprint Cup, Indy Car, and Champ Series races excluding qualifying and pre-race events.

Doesn't mention anything about being an open-air event...but the key that I didn't realize until now is WWE/MMA isn't in the listed organizations.

Strange, I could swear "open-air assembly" used to appear in there at some point. I'm on mobile so my research abilities are limited right now, but it looks like it used to be back in 2002 or so - the modern text as you listed doesn't have it.

Could it have something to do with advertising with banner tow? Certain organizations may get the TFR like nascar Sprint cup so that only certain aircraft can be flying the pattern with adverts (sprint, Goodyear, nbc etc)

Perhaps wrestlemainia doesn’t care who advertises during it and it’s not outside so